Enhanced oil recovery processes--thermal, micellar, and miscible or immiscible--are limited by depth, temperature, permeability, temperature, formation parameters, crude composition, fuel source, and many other factors. Carbon dioxide is usually classified as a miscible process but is not limited to such use. Carbon dioxide has been used in enhanced oil recovery operations in many situations: in sandstones, limestones, dolomites, and cherts; to depths of 10,800 feet with no known depth limitation; in formations with permeabilities of less than two millidarcys; at bottom hole temperatures of up to 248 degrees Fahrenheit with no known limitation; in formations varying from 8 feet to 600 feet in thickness and displaying appreciable heterogeneity; where crudes vary in specific gravities from 16 to 45 API; where crudes were displaced immiscibly; for crudes varying in viscosity from 0.3 to 188 centipoise; in reservoirs having oil saturations from 28 to 64 percent; and with well spacing up to over 50 acres per well.
Thus, enhanced recovery of oil using CO.sub.2 has been used for extreme ranges in the spectra of preferred criteria, and has been successfully used where other methods were ruled out because of factors such as unfavorable heterogeneity, permeability, oil gravity, and temperature. Although the most widely accepted theory of CO.sub.2 -enhanced recovery is based on the miscibility of CO.sub.2 in crudes, thereby decreasing viscosity, it is also reported that CO.sub.2 shows highly efficient immiscible displacement behavior.
The most important problem is finding an economical CO.sub.2 source. Current CO.sub.2 sources include power plant flue gases, cement plant and limestone plant flue gases, by-product of fertilizer and chemical plants, for example, ammonia plants, naturally occurring gas deposits, and the like. Highly desirable are sources of substantially pure CO.sub.2 which are available for direct use in the oil field. Such sources presently available include power plant flue gases after a carbon dioxide recovery step, ammonia plant stack gases, and naturally occurring gas deposits. Carbon dioxide by-product from fermentation industries has also been broadly suggested in the art. However, such sources have been previously rejected because of low availability coupled with high purification costs.
Single cell protein plants are prolific generators of carbon dioxide. However, in the design of single cell protein plants recurrent problems of providing effective gas exchange have been encountered. Briefly, the problems are: (1) to provide an adequate oxygen supply for optimum growth while avoiding oxygen levels which result in oxygen induced cell damage; (2) to adequately distribute the oxygen provided to the ferment; and (3) to maintain adequate flush out rates of carbon dioxide to avoid carbon dioxide inhibition of the ferment.
Accordingly, it is an object of this invention to provide an efficient source of substantially pure carbon dioxide. It is a further object of this invention to provide a method of single cell protein production capable of operating in large-scale under high cell density operations. It is a further object of this invention to operate a single cell protein plant intentionally to produce high pressure, relatively pure carbon dioxide. It is another object to operate such a plant to produce such carbon dioxide for enhanced oil recovery operations. Yet another object is to provide such a fermentation process which reduces compression costs and wastage of purified oxygen. Yet another object is such a process which is simple and well adapted for its intended purpose. Other objects and advantages of the instant invention will be apparent to one skilled in the art from the following description and drawing.